One configuration of an illumination circuit of a discharge lamp (e.g., a metal halide lamp) includes a DC power supply circuit having a a DC-DC converter; a DC-AC conversion circuit (i.e., an inverter circuit); and a starter circuit (i.e., a starter). According to one application of such a configuration, a DC voltage from a battery is converted to a desired voltage in the DC power supply circuit, and is further converted to an AC output voltage in the subsequent DC-AC conversion circuit. A start-up signal (a so-called starter pulse) is superposed thereon, and the superposed voltage is supplied to the discharge lamp (see, for example, Japanese patent document JP-A-7-142182).
However, a configuration where a voltage is converted through two stages (i. e., a DC-DC voltage conversion and a DC-AC conversion) is not suitable for reducing the size of a large circuit. Therefore, Other configurations have been suggested. For example, in one alternative configuration, an output whose voltage has been boosted by a single-stage voltage conversion in a DC-AC conversion circuit is supplied to a discharge lamp (see, e.g., Japanese patent document JP-A-7-169583).
Subsequently, a no-load voltage (hereinafter, referred to as “OCV”) before the discharge lamp is illuminated (i.e., during an extinction period) is controlled in such a manner that a start-up signal is generated and supplied to the discharge lamp, thereby causing the discharge lamp to illuminate.
Thereafter, operational control (i.e., switching control) of the DC-AC conversion circuit is conducted to cause a transition to a steady illumination state.
Conventional illumination circuits may have various problems. For example, a loss during an extinction period (i. e., under no load) of the discharge lamp may cause a decline in circuit efficiency. Smooth and reliable transition of the discharge lamp to a stable illumination state may be difficult or may require a complicated control configuration.